Continuous Dewatering Recirculation System with Integral Coal Combustion Residual High Flow Plate Separator

ABSTRACT

The system for a continuous dewatering recirculating for removing particulate such as coal combustion residue from a water stream. The system includes multiple dewatering and recirculation containers, each having a submerged flight conveyor and lamella settlings plate located therein, at least one dewatering and recirculation container receives ash water stream overflow.

FIELD OF INVENTION

The present invention relates to a system for continuous dewateringrecirculation in combination with an integral high flow plate separatorfor coal combustion residue and the like. Specifically, the presentinvention relates to a continuous dewatering recirculation systemincluding multiple retention vessels, wherein the system includeslamella plate assemblies. Preferably, this invention is directed towardssubmerged drag chain conveyor vessels which are used to remove suspendedsolids from combustion processes, e.g., coal combustion residue. Each ofthe submerged drag chain conveyor vessels involves the addition of highflow plate separators for the purpose of better reducing suspendedsolids. The addition of these separators allow for an improved system soas to support the use of clean water pumps as opposed to less efficientslurry pumps to recirculate the water to material intake points of thesystem. Thus, a superior continuous dewatering recirculation system withimproved efficiency is disclosed.

BACKGROUND OF THE INVENTION

The present invention generally relates to apparatus for separation ofsolids suspended in a liquid and, more particularly, to an improvedlamella-type gravity separator.

Settling tanks and clarifiers have been used for many years to separatesolids suspended in water and wastewater. Such approaches include simpleconcrete or steel tanks where water containing suspended solids flowedin, was retained for a predetermined length of time, and departed,substantially free of suspended solids. Various advancements were madeover the years to increase the efficiency of such apparatus; includingthe incorporation of sludge removal mechanisms, flocculators and sludgerecycle mechanisms. Settling tanks, however, are often directed tobiological waste and non-abrasive materials having a comparatively smallparticle size, and thus may be too expensive and insufficiently robustin handling a broad array of operating conditions and particle sizes.Moreover, such systems are often incapable of handling non-ambient fluidstreams, such as coal combustion residue water streams.

In recent years, the separation art has included applications of lamellaseparation. Lamella separation separates solids from a carrying liquidby directing the liquid between series of inclined plates (lamellae).The effective settling area of each lamella plate is equivalent to thehorizontal projection of that lamella plate. Lamella plates aretypically spaced a few inches apart, with the result that large settlingsurfaces are concentrated within a relatively small area. The lamellaseparation promotes laminar flow conditions systems where they are used,which leads to a very high degree of separation. However, suchapplications are typically impractical for variable flow applicationswhere an adjustment in volume or weir height may be needed. Furthermore,some lamella plate applications may require a high number of lamellaplates which may be impractical from the viewpoint of cost and/oroperation.

Thus, the present state of the art reflects a need for a system whichreliably and efficiently processes coal combustion residue in acontinuous dewatering recirculation system while reducing or eliminatingany reliance upon a clarifier or other expensive equipment.

DESCRIPTION OF THE PRIOR ART

Examples of existing proposed designs of lamella separator apparatus aredisclosed in U.S. Pat. Nos. 3,552,554; 3,706,384; 3,894,955; 4,290,898,4,681,683, and 4,889,624. Such prior art, however, does not teach theuse of lamella technology in variable flow application for the removalof particulate (like coal combustion residue) in a continuous dewateringrecirculation system.

US 20110226194 A1 teaches a submerged scraper conveyor (SSC) consistingof a conventional SSC modified to include a slurry processing system,the system including a pair of overflow troughs and associated weirslocated exterior to and along the top edge of each side of thehorizontal section of the SSC and an underflow baffle. Nothing in thisreference, however, teaches or suggests usage with any lamella separatorapparatus, much less a system having adjustable weirs or other flowcontrol mechanisms for such systems as disclosed in the presentinvention.

What is needed is robust, cost effective solution for a continuousdewatering circulation system that enables efficient separation undervariable flow conditions.

DEFINITION OF TERMS

The following terms are used in the claims of the patent as filed andare intended to have their broadest plain and ordinary meaningconsistent with the requirements of the law.

A “coal combustion residue water stream” means a solid/liquid phasemixture with the solids generally comprising 1-40% by weight, the solidsgenerally having a specific gravity from approximately 0.5-3.0, and sizedistributions ranging from submicron particles up to about 1″. Thesolids comprise typically silica and alumina based compounds.

A “continuous dewatering and recirculation container” means a containerthat includes structures for enabling the continuous filtering, removaland dewatering of particulate contained with the coal combustion residuewater stream.

A “variable water level surge tank” can include—but is not limited to—aredundant continuous dewatering and recirculation container. Thevariable water level surge tank operates to adjust the continuousdewatering and recirculation system so as to maintain a substantiallyconstant volume in a companion continuous dewatering and recirculationcontainer in response to changes of flow streams.

“Filtering” means separation of solid coal combustion residueparticulate from the coal combustion residue water stream.

“Lamella settling plates” means a series of generally parallel platesdesigned to improve filtering of solids by reducing turbulence.

“The number of plates” is a factor which may be influenced by parameterssuch as the flow rate, specific gravity and particle size distributionof the coal combustion residue water stream, and the geometry of theplates.

“The geometry of the plates” is a factor which may be influenced by thecontainer height and cross-section, the desired modularity and/or easeof removal for maintenance, and the desired efficiency of the plates insitu.

The “Reynolds number” is a dimensionless number that is a ratio ofmomentum or inertial force to viscous forces. It is used to characterizedifferent flow regimes within a similar fluid, such as laminar orturbulent flow. A Reynolds number may be approximated by knowing theflow rate of the coal combustion residue water, the number of lamellaplates, the plate spacing, and width of the plates, and knowing theapproximate density and viscosity of the coal combustion residue waterstream as understood by those of skill in the art.

An “energy dissipating baffle” is a structure for dissipating momentumin the coal combustion residue water stream upon entering the container.

An “adjustable height weir” means a device to ensure equal distributionflow amongst the lamella plates.

A “drag chain” refers to a chain which generally removes filtered coalcombustion residue solids from the bottom of the container. It generallyincludes two chain strands with a structure attached in between (e.g.,flights, plates or the like) that are equally spaced throughout whichdrag the solids up and out of the container for further processing.

“Substantially constant water level” means that the height of the waterwithin a given container is relatively unchanged due despite adjustmentsmade in the coal combustion residue water stream flow. (e.g., within 8inches constancy from front to back in a container of 100 feet).

Where alternative meanings are possible, the broadest meaning isintended. All words used in the claims set forth below are intended tobe used in the normal, customary usage of grammar and the Englishlanguage.

OBJECTS AND SUMMARY OF THE INVENTION

The apparatus and method of the present invention generally includes asystem for reducing the particulate in a bottom ash water stream. Thecomponents of the systems generally include at least two continuousdewatering and recirculation containers, with each container containinga submerged flight conveyor therein, and each container includinglamella plates therein. At least one of the containers is configured toreceive coal combustion residue water stream overflow from another ofthe continuous dewatering and recirculation containers, and the systemincludes a control mechanism for selecting which container receives ashwater stream overflow.

Different, alternative structures from the above described summary arealso within the scope of the inventions of the present application. Forinstance, the present invention may cover systems including only asingle dewatering and recirculation container with a surge tank forhandling overflow. In such a configuration, only the single tank wouldrequire lamella plates and a drag chain, and there would be no need fora control or selection mechanism. Still further alternatives to theabove examples include adjustable height weirs connected the lamellasettling plates so as to adjust the height of the water in the containerso as to improve the efficiency of the filtering by the lamella settlingplates.

The immediate application of a present invention will be seen inprocessing coal combustion residue water streams from operating plants,though those of skill will see that the present invention could beapplied to other fields (e.g., bio-mass) requiring a robust and costeffective solution for continuous dewatering recirculation.

Thus can be seen that one object of the present invention is to providea cost effective system for reducing particulate in a coal combustionresidue water stream.

A further object of the present invention is to provide a system using alamella separation process on a non-laminar flow stream.

Still another object of the present invention is to provide a lamellaprocess on a variable flow rate system.

Yet another object of the present invention is to provide for a systemwhich eliminates the need for a clarifier in a continuous dewateringrecirculation system using a fresh water pump.

Still another object of the present invention is to provide a systememploying an adjustable weir for a lamella separation process

Another object of the present invention is to provide a selectableoverflow configuration for a continuous dewatering and recirculationsystem.

It should be noted that not every embodiment of the claimed inventionwill accomplish each of the objects of the invention set forth above. Inaddition, further objects of the invention will become apparent based onthe summary of the invention, the detailed description of preferredembodiments, and as illustrated in the accompanying drawings. Suchobjects, features, and advantages of the present invention will becomemore apparent in light of the following detailed description of a bestmode embodiment thereof, and as illustrated in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a continuous dewatering circulationsystem in accord with a first embodiment of the present invention.

FIG. 2 shows a first cross section view of the continuous dewateringcirculation system in accord with a first embodiment of the presentinvention taken along section line 2-2 in FIG. 1.

FIG. 3 shows a second cross section view of the continuous dewateringcirculation system in accord with a first embodiment of the presentinvention taken along section line 3-3 in FIG. 1.

FIG. 4 is a detail view of the adjustable weir feature in conjunctionwith a detail of lamella plates in accord with another embodiment of thepresent invention that is shown in FIG. 3 taken along detail circle 4.

DETAILED DESCRIPTION OF THE INVENTION

Set forth below is a description of what is currently believed to be thepreferred embodiment or best examples of the invention claimed. Futureand present alternatives and modifications to this preferred embodimentare contemplated. Any alternatives or modifications which makeinsubstantial changes in function, in purpose, in structure or in resultare intended to be covered by the claims in this patent.

FIG. 1 shows a first preferred embodiment constructed in accordance withthe present invention. The continuous dewatering system 10 includes abottom ash hopper 20, a first continuous dewatering and recirculationcontainer 30 and a second continuous dewatering and recirculationcontainer 40. A recirculation system of this type is appropriate wherehigh conveying capacities are required and minimal outage time is neededfor conversion. Each of the continuous dewatering and recirculationcontainers 30, 40 in this embodiment include a submerged flight conveyor32, 42 including a drag chain 34, 44 for ash particulate from the coalcombustion residue water stream received from the bottom ash hopper 20.Each of the dewatering and recirculation containers 30, 40 furtherincludes sets of lamella plates 36, 46 which are responsible forremoving the ash/coal combustion residue from the coal combustionresidue water stream.

In practice, the coal combustion residue water stream is pumped from thebottom ash hopper 20 via a pump 50 through piping 52. The typical flowrates for systems practicing the present invention is at least 2000gallons per minute, with a typical flow range being from approximately2000-9000 gallons per minute. The piping 52 splits into a tee deliveryconfiguration, with each of the ends of the tee feeding into therespective continuous dewatering and recirculation containers 30, 40.The control of which continuous dewatering and recirculation containerreceives the coal combustion residue water stream is enabled by acontrol unit (not shown) and/or direct, manual control of valves 54, 56,which control the flow of the coal combustion residue water stream. Asshown in the example of FIG. 1, continuous dewatering and recirculationcontainer 30 is receiving the coal combustion residue water stream, butcontinuous dewatering and recirculation container 40 is not.

As shown in FIG. 2, the coal combustion residue water stream isdelivered out of the ends of the T of piping 52 and impacts upon anenergy dissipating baffle 58, 60, which works in conjunction with aflocculant injection tube 62, 64. The flocculant injection tube 62, 64selectively add a limited amount of flocculant to the coal combustionresidual water to better separate particulate from the water stream andto enable removal of larger particles from the stream such that they arecaptured by the flights or plates 66 of the drag chain 34, 44 so as tobe removed from the stream. Furthermore, the speed of the drag chain 34,44 is optionally adjustable, for instance, in response to the rate ofsolids entering the containers 30, 40.

As shown in FIG. 3, the present embodiment further removes particulatefrom the coal combustion residue water stream as the stream travels downthe length of the continuous dewatering and recirculation containers 30,40 by interacting with the sets of lamella plates 36, 46. These sets ofplates typically comprise between 150 and 1000 plates for eachcontinuous dewatering and recirculation container 30, 40, and arefurther typically spaced on the order of two inches apart or more fromone another and are preferably angled around 60 degrees from thehorizontal (bottom) of the continuous dewatering and recirculationcontainers 30, 40. Those of skill in the art will understand that theflow of the coal combustion residue water stream, and the number andgeometry of plates in the plurality of lamella settling plates, 36, 46will influence the degree of turbulence. In fact, even using a high flowrate of the coal combustion residue water stream, and employing thenumber and geometry of plates a described above, the practice of thepresent invention is nonetheless believed to operate with advantagedespite having a turbulent fluid regime (i.e., a Reynolds number of500+) within the region of lamella settling plates 36, 46.

One important feature in this embodiment in the present invention, asshown in FIG. 3, is the ability to control the level of the coalcombustion residue water stream in at least one of the continuousdewatering and recirculation containers 30, 40, i.e., in order tomaintain the efficacy of the lamella plates 36, 46. The structures usedfor maintaining a substantially constant water level along the length ofthe continuous dewatering and recirculation containers 30, 40 areoverflow crossovers 72, 74 and valves 76, 78. These structures enablethe system 10 to handle changes in the flow rate of the coal combustionresidue water stream while maintaining a constant water level for thecontainer (30 or 40) selected for receiving the coal combustion residuewater stream in the first instance (i.e., container 30 in the example ofFIG. 1). This constancy in water level provides for improved efficiencyof system 10 whereby the lamella plates 36, 46 can settle or filterfurther particulate in down into the bottom of the containers 30, 40 soas to be captured by the flights or plates 66 of the drag chain 34, 44for removal. As shown in FIG. 1, the water from the now cleaned coalcombustion residue water stream is removed from the containers 30, 40through clean water supply piping 80, and selectively passed throughvalves 82, 84 for recirculation in the system 10.

Optionally, a further feature that can be used in alternativeembodiments of the present invention to incorporates an adjustable weir90 with integral overflow troughs 91, as shown in FIG. 4. The adjustableweir 90, allows for the overflow to be balanced among several modules ofplates 36, 46 in the overall system 10. This weir 90 is designed foroverflow from the sides of the plates 36, 46 (rather than over the topas implemented on existing technology). The weir 90 can also incorporatescreens 92 to handle larger buoyant particles or floaters.

The above description is not intended to limit the meaning of the wordsused in the following claims that define the invention. Rather, it iscontemplated that future modifications in structure, function or resultwill exist that are not substantial changes and that all suchinsubstantial changes in what is claimed are intended to be covered bythe claims. For instance, the present invention could be employed in asystem including just a single container 30 in conjunction with a surgetank (not shown). In addition, the present invention could operate withthree or more containers, and can further include a sun shield for thecontainers to protect from UV exposure and/or structures to enable theplates 36, 46 to be used in a modular fashion and to be walked uponduring use. Likewise, it will be appreciated by those skilled in the artthat various changes, additions, omissions, and modifications can bemade to the illustrated embodiments without departing from the spirit ofthe present invention. All such modifications and changes are intendedto be covered by the following claims.

We claim:
 1. A system for reducing the particulate in a bottom ash waterstream comprising: a) A plurality of continuous dewatering andrecirculation containers, each of the plurality of continuous dewateringand recirculation containers containing a submerged flight conveyortherein, with at least one of the plurality of continuous dewatering andrecirculation containers receiving coal combustion residue water streamoverflow from another of the plurality of continuous dewatering andrecirculation containers; b) At least one lamella settling plate locatedwithin each of the plurality of continuous dewatering and recirculationcontainers; and c) A control unit for selecting at least one continuousdewatering and recirculation container from among the plurality ofcontinuous dewatering and recirculation containers for receiving ashwater stream overflow.
 2. A system for reducing the particulate in acoal combustion residue water stream of at least 2000 gallons per minutecomprising: a) At least one continuous dewatering and recirculationcontainer for receiving the coal combustion residue water stream; b) Atleast one variable water level surge tank operatively connected to theat least one continuous dewatering and recirculation container so as tomaintain a substantially constant water level therein for filtering thecoal combustion residue water stream; c) A plurality of lamella settlingplates located within the continuous dewatering and recirculationcontainers for filtering the coal combustion residue water stream,wherein the flow of the coal combustion residue water stream, the numberand geometry of plates in the plurality of lamella settling platesgenerates a Reynolds number within the plurality of lamella settlingplates of at least
 500. 3. The continuous dewatering and recirculationsystem of claim 2, wherein the plurality of lamella settling platescomprises between 150 and 1000 plates for each continuous dewatering andrecirculation container.
 4. The continuous dewatering and recirculationsystem of claim 2, wherein the spacing between at least two neighboringplates in the plurality of lamella settling plates is at least 2 inches.5. The continuous dewatering and recirculation system of claim 2,wherein the geometry of at least some of the plates in the plurality oflamella settling plates includes a slope of at least 60 degrees.
 6. Thecontinuous dewatering and recirculation system of claim 2, wherein thegeometry of at least some of the plates in the plurality of lamellaplates is 4×4 feet.
 7. The continuous dewatering and recirculationsystem of claim 2, wherein the plurality of lamella settling plates cangenerate a non-laminar flow for a coal combustion residue water streamranging from 2000-9000 gallons per minute.
 8. The continuous dewateringand recirculation system of claim 2 further comprising adjustable heightweirs connected the plurality of lamella settling plates so as to adjustthe height of the water in the container so as to improve the efficiencyof the filtering by the plurality of lamella settling plates.
 9. Thecontinuous dewatering and recirculation system of claim 8 furthercomprising a screen attached to the adjustable height weir to filterlarger, buoyant particles from the coal combustion residue water stream.10. A continuous dewatering and recirculation system for reducing theparticulate in a coal combustion residue water stream of at least 2000gallons per minute comprising: a) A first and second containeroperatively connected to one another for receiving the coal combustionresidue water stream, wherein the second container is capable of bothsecondarily filtering particulate in a coal combustion residue waterstream, and maintaining a substantially constant water level in thefirst container for filtering the coal combustion residue water stream,and the first and second containers may be switched in operation suchthat the first container is capable of maintaining a substantiallyconstant water level in the second container for filtering the coalcombustion residue water stream; b) A conveyor system in the each of thefirst and second container for dewatering and removing settledparticulate therefrom; and c) A plurality of lamella settling plateslocated within each of the first and second continuous dewatering andrecirculation containers for filtering the coal combustion residue waterstream, wherein the flow of the coal combustion residue water stream,the number and geometry of plates in the plurality of lamella settlingplates generates a Reynolds number within the plurality of lamellasettling plates of at least
 500. 11. The continuous dewatering andrecirculation system of claim 10, wherein the conveyor system comprisesa drag chain.
 12. The continuous dewatering and recirculation system ofclaim of claim 11, further comprising a control unit for adjusting thespeed of the drag chain in response to the rate of solids entering thefirst and second containers.
 13. The continuous dewatering andrecirculation system of claim 12, wherein the control unit measuresvalues corresponding to the force on the chain.
 14. The continuousdewatering and recirculation system of claim 10, wherein the first andsecond container each include an energy dissipating baffle located at aninlet for receiving the coal combustion residue water stream.
 15. Thecontinuous dewatering and recirculation system of claim 10, wherein thefirst and second container each include a further inlet port adjacentthe energy dissipating baffle for receiving a flocculant to mix with thecoal combustion residue water stream prior to filtering by the pluralityof lamella settling plates.
 16. The continuous dewatering andrecirculation system of claim 10, containing an inlet pipe connected tothe first and second containers, the inlet pipe providing a coalcombustion residue water stream and a coagulant from a location remotefrom the first and second containers.
 17. The continuous dewatering andrecirculation system of claim 11, wherein each of the first and secondcontainers includes a separate drag chain so as to create separate pilesof particulate removed from each of the first and second containers soas to enable further dewatering.